This invention relates to a battery circuit adapted to control connection between a main circuit of an integrated circuit (IC) memory card or, more specifically, a random access memory card and a battery incorporated in the card.
FIG. 1 shows a block diagram of the construction of a conventional random access memory card (hereinafter referred to as "RAM card") which is described in "IC Memory Card Guideline" (published in September 1986) edited by a personal computer affairs committee of Nippon Denshi Kogyo Shinko Kyokai, a corporation. Referring to FIG. 1, a RAM chip section 2 is normally constituted by a plurality of static RAMs. An interface connector 1 is provided for connection to an IC card terminal (not shown). A control line 4 and an address line 5 connect the interface connector 1 to the RAM chip section 2 through a chip selection control circuit 3 adapted to select a designated one of the static RAMs of the RAM chip section 2. A data line 6 is directly connected between the interface connector 1 and the RAM chip section 2. An external power supply line 1 and a ground line for connection to a power source provided outside the RAM card via the interface connector 1 are connected to a power supply control circuit 10 to which is also connected a power supply line 9a extending from a data backup battery 9 (hereinafter referred to simply as "battery") to keep data stored in the RAM chip section 2 during the time when the RAM card is detached from the IC card terminal and when it cannot be supplied with power from the outside. The power supply control circuit 10 operates to supply power from the external power supply line 11 or the battery 9 to the RAM chip section 2 and to the chip selection control circuit 3 via a power supply line 13. Ordinarily, the voltage Vbb of the battery 9 is about 3V while the voltage Vcc at the external power supply line 11 is about 5V when the RAM card is supplied with power from external power source. There are two types of RAM cards depending upon the period of time in which the battery 9 is available: one in which the battery 9 is completely embedded and cannot be replaced, that is, a throwaway type card; and one in which the used battery can be easily replaced with a new one. Generally, RAM cards of a small capacity are of the embedding type while RAM cards of a large capacity are of the battery-replaceable type.
FIG. 2 shows one of simplest examples of the battery circuit of the RAM card shown in FIG. 1 in order to explain fundamental functions thereof. In FIG. 2, components identical to those shown in FIG. 1 are indicated by the same reference characters. A battery circuit 20 has a diode 14 for preventing a battery current leak from the battery 9 to the outside of the RAM card, and a diode 15 for preventing the battery from being charged via the outside power supply line 11. By the function of these two diodes, one of the voltage Vcc of the external power supply line 11 and the voltage Vbb of the battery 9 is selected as an internal voltage Vdd. Thus, this circuit constitutes the simplest example of the control circuit 10. As mentioned above, in a large-capacity RAM card, the RAM chip section 2 includes a multiplicity of static RAMs, and the backup current flowing out of the battery 9 is large. In this case, therefore, the life of battery 9 is short. For this reason, such RAMs are ordinarily of the battery-replaceable type.
FIG. 3 is a circuit diagram for illustration of a state in which the battery 9 is packaged separately from the RAM card body 21 (represented by the battery circuit when shipped (forwarded) from the manufacturer, and FIG. 4 is also a circuit diagram for illustration of a state in which the battery 9 is attached to the RAM card body 21 when the RAM card body 21 and the battery 9 are taken out of the packagings so that they can be used. In the case where the RAM card will not be used for a long period of time and there is no need to maintain the data stored in the RAM card, the battery 9 is detached from the RAM card body 21 in order to avoid reduction in the life of the battery 9.
In the case of a RAM card having the thus-constructed conventional battery circuit, it is undesirable in terms of battery life to previously attach the battery to the RAM card body at the time of forwarding, and it is therefore necessary to pack up the battery and the RAM card body separately from each other. In addition, in the case where the RAM card will not be used for a long period of time and where there is no need to maintain data stored in the RAM card, the battery must be detached from the RAM card, thus necessitating troublesome operations.